update the submodule to fix the plotting issue

Jason Ramapuram · Jason Ramapuram · commit 68c8bfd1eba7 · 2015-09-28T11:39:32.000+02:00
diff --git a/arrayfire b/arrayfire
@@ -1 +1 @@
-Subproject commit 2d756722341358448106302eb58a9e25fcf86574
+Subproject commit 31d247584d15d5bf352438c4a6c4ef11b5170590
